This goes against all evidence I have seen for folks who have lost a drastic amount of weight very rapidly. Bodybuilders seem to see the same effect as well when on cuts.

When you are losing 5% of your bodyweight per month (as I was, and many do) a substantial portion of that is simply going to be mean muscle mass. You can counteract some, but not all, of this by heavy resistance training. It's very difficult to not lose muscle mass while losing weight - it takes extreme measures for most folks (e.g. athletes) to do so.